Synthesis of high density polymer arrays on a microarray chip is known. Examples of such high density polymer arrays include nucleic acid arrays, peptide arrays, and carbohydrate arrays.
One method of preparing polymer arrays on microarray chips involves photolithographic techniques using photocleavable protecting groups (FIG. 1). For example, the method includes attaching photoreactive groups to the surface of a substrate, exposing selected regions of the substrate to light to activate those regions, attaching a monomer with a photoremovable group to the activated regions, and repeating the steps of activation and attachment until macromolecules of the desired length and sequence are synthesized. However, the devices made by the photolithographic methods are not scalable to sub 1 μm features due to the limitation in synthesis and optical detection. Typically molecular recognition events are detected through optical readout of fluorescent labels attached to target molecules specifically bound to the probe molecules. Thus, the detection of molecular recognition events is difficult to implement and miniaturize, relies on the use of optical labels, and requires large or expensive instrumentation.
Additional methods and techniques applicable to polymer array synthesis include electrochemical synthesis. One example includes providing a porous substrate with an electrode therein, placing a molecule having a protected chemical group in proximity of the porous substrate, placing a buffering solution in contact with the electrode and the porous substrate to prevent electrochemically generated reagents from leaving the locality of the electrode (the use of confinement electrodes to prevent reagents from diffusing away have also been described), applying a potential to the electrode to generate electrochemical reagents capable of deprotecting the protected chemical functional group of the molecule, attaching the deprotected chemical functional group to the porous substrate or a molecule on the substrate, and repeating the above steps until polymers of the desired length and sequence are synthesized.
One manufacturer produces devices with electrochemical synthesis on planar Pt electrodes and optical detection. Scalability and sensitivity of these devices are poor. Enzymatic current is measured on the electrode arrays. However, this technique does not have on-die amplification. The device density is also low (1K or 12K electrodes) and current measurements are limited in sensitivity to pA ranges.
High-density DNA microarray chips have been useful tools for probing deep and wide-ranging questions in biology, but they can't track protein activities. Although DNA chips can be fabricated and stored dry for long periods of time, the formation of high-density protein chips to fully understand protein functions has so far been a tremendous challenge. This is because proteins need to be in a wet environment in order to remain structurally intact and carry out their biological functions. Despite the serious effort and progress made in fabrication techniques, this requirement is still a barrier to the development and use of suitable protein chips. The embodiments of the invention overcome this barrier.